This invention relates to a method of facing a substrate, a facing body for facing a substrate and a kit for facing a substrate. The method, body and kit ensure or obtain an improved degree of adhesion between the substrate and the facing body, which may be done, for example, to improve the wear resistance of faced surfaces, and in a convenient and easily employed way.
It is known to apply hard facing materials to surfaces of components, tools and implements which may be subject to wear in order to improve their wear resistant or cutting properties. An example of a hard facing material is tungsten carbide, which, in a known process, is positioned on a metal surface and then fixed in place by means typically of brazing, or soldering onto the surface. Usually, the tungsten carbide is in the form of small regular shaped blocks, often referred to as tips or inserts.
WO-A-9527588 discloses a method for facing a substrate, for example, a stabiliser for a drill string, using such tungsten carbide blocks of rectangular shape having sides of about 13 mmxc3x975 mm and thicknesses of 3 mm. The entire contents of WO-A-9527588 are incorporated by reference herein for all purposes.
In WO-A-9527588, the following steps in a method of facing a substrate are described:
a) Tungsten carbide blocks are first treated by spraying, on a contact surface thereof, a layer of nickel alloy of about 0.25 mm thick.
b) The tungsten carbide blocks are then placed, with their sprayed faces being directed towards the substrate, in holes in a perforated mat of rubber. The holes are shaped so that the blocks form an interference fit therein. Typically the mat is of rectangular shape with sides 10 cm by 15 cm and a thickness of 3 mm. The mat conventionally comprises from 10 to 1,000 holes for the reception of the tungsten carbide blocks.
c) The flexible mat is then positioned upon the surface of the substrate, for example, a stabiliser, fishing tool or any other surface, whereupon it substantially conforms to the shape thereof whilst at the same time retaining each of the tungsten carbide blocks in a predetermined location.
d) The blocks are then each welded to the substrate using an electrical welding machine, the machine being set to apply a voltage of 75 volts and a current of 5000 amps to produce a weld joint or connection.
e) After the blocks have been welded to the substrate surface, the mat is removed, the substrate is heated to a temperature of between 80xc2x0 C. and 150xc2x0 C. (preferably about 125xc2x0 C.) and sprayed with a nickel alloy to a thickness of 0.25 mm. The purpose of this is to reduce susceptibility to oxidation during subsequent processing.
f) The substrate is then further heated to a temperature of between 200xc2x0 C. and 400xc2x0 C. (preferably about 250xc2x0 C.) and the entire surface is again sprayed with a nickel alloy until a layer of thickness about 3.5 mm has been built up; during spraying the temperature of the area around each block is raised to between 1050xc2x0 C. and 1150xc2x0 C. so that the alloy fuses.
The faces of the tungsten carbide blocks which contact the substrate, (hereinafter known as contact faces thereof), are substantially planar and make only a single point contact with the substrate if the substrate is curved. It will be appreciated that a substantially triangular void will be formed between the contact face and the substrate. This substantially triangular shaped void is filled with molten metal during the fusing process.
Furthermore, when using relatively large inserts, or when working with a flat substrate, the quality of the weld is unreliable due to the large areas of contact between the insert and the substrate and therefore the variable current density at the contact points and hence the temperature generated by resistance heating. In addition, the braze thickness is inconsistent.
Moreover, it has been facing that arcing can sometimes occur between those portions of the contact face and the substrate which have sufficient proximity to one another but which are not in contact with one another. This in turn reduces the quality of the weld as the welding current is distributed over a larger than desirable area.
Furthermore, step a) above is required in order to ensure that there is brazing material between the contact face of each block and the substrate, while step b) can be awkward and time consuming.
It is an object of the present invention to mitigate the problems of the prior art.
Accordingly, the present invention provides a method of facing a substrate comprising the steps of:
a) applying a plurality of facing bodies to a carrier in a pattern corresponding to the desired pattern of the bodies of the faced substrate, the carrier having holes positioned substantially centrally with respect to each body and each body having, on a contact face thereof to be fixed to said substrate, raised weld elements which serve to locate said contact face substantially parallel and spaced from the substrate;
b) applying the carrier to the substrate with said contact faces of the bodies facing the substrate;
c) electrically welding each body to the substrate by applying a welding tip to the body exposed through said hole, said weld elements ensuring that a gap remains between said contact face and substrate after welding; and
d) brazing said bodies to said substrate so that brazing material flows between said bodies and the substrate.
Preferably, said bodies have a first face opposite said contact face, which first face is adhered to one side of said carrier. In which case, preferably, the method further comprises the step of:
e) before step d) above, peeling the carrier from the first faces of the bodies, step a) above including the step adhering with the releasable adhesive. Preferably, said carrier is paper. Alternatively, said carrier may be burnt off before step d).
Alternatively, said carrier may comprise a perforated rubber mat, said bodies being pressed into and retained by respective perforations which correspond in size and shape with the bodies.
The method preferably further comprises the step of:
f) before step d) above, but after step e) if applicable, heating the bodies and the substrate to a temperature of between 80xc2x0 C. and 150xc2x0 C. (preferably about 125xc2x0 C.) and spraying with a stabiliser to inhibit oxidation. Said stabiliser may comprise a nickel alloy or a fluxing agent, and may be about 0.25 mm thick.
The method preferably further comprises the steps of:
g) after step f) above, further heating the bodies on the substrate to a temperature of between 200xc2x0 C. and 400xc2x0 C. (preferably about 250xc2x0 C.) and spraying with braze material, preferably a nickel alloy; and wherein step d) above comprises fusing the alloy at a temperature of between 1050xc2x0 C. and 1150xc2x0 C.
Such a method has numerous advantages. An improved current path is created by the raised weld elements which reproducibly determines the contact between the bodies and the substrate. This consequently improves and makes more consistent the weld of the body to the substrate. Moreover, a consistent gap is left between the contact face and the substrate after welding so that the braze is drawn under the bodies by capillary action and the amount of braze is balanced. That is to say, with a flat substrate, the braze will reliably be of even thickness.
Moreover, because a gap is reliably produced for the braze material to be introduced under the bodies, step a) of the prior art method mentioned above can be eliminated. As a result, the carrier can be made of paper or card and the bodies can be adhered thereto as a first step in an automated process. On the other hand, the bodies could still be supplied loose for insertion in a rubber mat, as described in WO-A-9527588.
Accordingly, a second aspect of the present invention provides a facing body suitable for facing a fishing tool or drill string stabiliser for use in oil and gas industry drilling, comprising a body having a contact face and a working face opposite the contact face, wherein the contact face comprises spaced raised weld elements which serve to locate said contact face substantially parallel and spaced from a substrate to which the body is adapted to be fixed.
In a third aspect, the present invention provides a facing kit for facing a substrate comprising a carrier with facing bodies adhered by a first face thereof to the carrier in a pattern corresponding to the desired pattern of the bodies on the faced substrate, holes in the carrier each exposing substantially the centre of said first face of respective ones of said bodies, and the bodies having on a contact face thereof to be fixed to the substrate raised weld elements serving to locate said contact face substantially parallel and spaced from the substrate when the strip is applied thereto.
Preferably a peelable heat shrink layer is applied to the bodies and adhered to the carrier around the bodies. This ensures that the bodies are not dislodged from the carrier during transportation. Preferably each hole does not extend beyond the boundaries of said respective first face. The carrier may be a strip of paper or card.
Thus, step b) above of the prior art method is eliminated, at least in terms of a manual task to be completed at the point of application of the bodies to the substrate. Instead, this step can be automated and the bodies can be supplied to the person facing the substrate already adhered to the carrier. This is possible because, as mentioned above, step a) has been eliminated; which step would otherwise destroy the carrier given the temperatures involved in that spraying step. Moreover, the substrate facing bodies on the carrier can therefore be positioned on the substrate before being brazed to the substrate when both the substrate and the body are at room temperature. That is to say, there is no loss of heat which occurs between steps a) and b) of the prior art, since the rubber mat can only be loaded with blocks once they have cooled after step a). Thus, the overall energy required to fix the body to the substrate is reduced as compared to the prior art.
The present invention also increases the current density during welding, that is, by focusing the available current through the weld elements and so as to achieve good adherence. The reduction in the current required to produce an acceptable weld also leads to a reduction in the risk of damage to the first face of the insert.
An embodiment is provided wherein said raised weld elements comprise a plurality of raised dimples. Preferably said raised dimples have a radius of curvature of about 0.085 inches (2.159 mm). The diameter of said raised dimples is substantially 0.08 inches (2.032 mm). Preferably said raised dimples have a height of between substantially 0.001 inches (0.0254 mm) and 0.039 inches (1 mm). Three dimples are preferably provided, preferably defining the corners of an equilateral triangle.
Alternatively said raised weld elements may comprise a plurality of raised lines. Preferably said raised lines have a radius of curvature of 0.01 inches (0.254 mm). Typically the raised lines have a height of 0.01 inches (0.254 mm) and a width of 0.02 inches (0.508 mm). Alternatively, the raised lines have a substantially flat contact surface.
Each body may comprise a cuboid; in which case, the raised lines may be disposed parallel to one of the sides of the body or span the width or length of the body. Alternatively, the raised lines may be arcuate or substantially circular, and even concentric. The raised lines may have a substantially flat bottom surface.
Each body may comprise a substantially cylindrical peripheral side wall or a substantially triangular peripheral side wall. The side wall may be tapered. Advantageously, the tapered wall provides a positive cutting geometry. The side wall has a height of 0.02 inches (5.08 mm) or 0.25 inches (6.35 mm).
Although it is within the ambit of the present invention to apply the bodies to a rubber mat, one of the disadvantages of this arrangement is that the mat surrounding each body can be no thicker than the spacing required for the bodies on the surface to be faced. In fishing tools for the oil and gas drilling industry, the spacing between adjacent bodies should be very small, and preferably almost zero, so that use of the rubber mat is substantially impractical. On the other hand, in drill string stabilisers, the separation between facing bodies can be much larger, in which event the use of a rubber mat, while less convenient than a paper carrier, is still perfectly feasible.